Mercury methylation by microorganisms: from cell to environment – MicroMer
Mercury (Hg) is a global pollutant, able to be converted into highly neurotoxic monomethylmercury (MMHg), a compound bioaccumulated and bioamplified in food webs. Microorganisms regulate environmental MMHg level, by controlling directly inorganic Hg (IHg) methylation and MMHg degradation or indirectly through redox transformations controlling Hg bioavailability. Understanding the biotransformation processes of Hg in the environment is a key component of risk assessment of Hg in ecosystems and human health. However, there is little knowledge on the cellular processes leading to MMHg production. It is of special interest to develop studies at a cellular level to understand Hg transformations in terms of genetic determinism, cellular pathways and environmental factors regulating them.
The MicroMer project aims to characterize the process of Hg methylation and demethylation at cellular level and environmental level. At cellular level, MicroMer aims to determine 1) the speciation of Hg in the cell environment favoring Hg transformations, 2) the mechanisms of Hg recognition by the cell, 3) the intracellular steps of Hg speciation and, 4) the Hg species export from the cell. Our hypothesis is that methylation and demethylation processes are coupled and that they are driven by Hg uptake but also its export. Thus, we intend to decipher the role of Hg cell trafficking and Hg speciation (in the extracellular and intracellular compartments) in Hg transformations. The processes will be investigated in Sulfate Reducing Bacteria models, Pseudodesulfovibrio hydrargyri BerOc1, able to methylate IHg and demethylate MMHg and two other strains able only to demethylate MMHg: Pseudodesulfovibrio piezophilus C1TLV30 and Desulfovibrio alaskensis G20. P. hydrargyri BercOc1 mutants of either Hg methylation, sensing, and export, and their heterologous expression in C1TLV30 and G20 will be performed. By experimental evolution, we will also generate BerOc1 strains with higher methylation and demethylation capacities. The consequences of mutations in 1) Hg methylation and demethylation, 2) Hg speciation and nature of Hg ligands (thiols), and 3) localization will be determined. MicroMer explores an outstanding and original line of work to understand Hg transformation based on our solid previous results. The striking combination of genetics, bacterial physiology and imaging methods (nano X-ray fluorescence, and electron microscopy) coupled with X-ray absorption spectroscopy and hyphenated mass spectrometry techniques is, to our knowledge, unique and innovative, and will forcefully bring new results and perspectives in the understanding of Hg methylation and demethylation. The MicroMer project has also an environmental scope that aims to determine the representativeness of the mechanism described in our model strains. By applying metagenomics and metatranscriptomics in a time-dependent (daily and seasonally) approaches, we will determine the fate of our model strain in its original environment. In parallel, we will determine the diversity and expression of major genetic determinisms in order to gain an overview of the representativeness of the model deciphered in MicroMer project in a natural environment.
The MicroMer project proposes extensive and collaborative studies on mercury transformations mediated by bacteria using interdisciplinary approaches (molecular genetics, microbial physiology, analytical chemistry, X-ray absorption spectroscopy, imaging and microbial ecology). The project unites research teams (IPREM, MIO, and BIC) with strong expertise on those approaches in order to shed light on challenging topic. The environmental and health implications of the expected data obtained in this basic research project are of major interest. They will provide key information about the highly toxic MMHg production that is essential for risk evaluation, management, and sustainable development.
Madame Marisol GONI-URIZZA (INSTITUT DES SCIENCES ANALYTIQUES ET DE PHYSICO-CHIMIE POUR L'ENVIRONNEMENT ET LES MATERIAUX)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
IPREM INSTITUT DES SCIENCES ANALYTIQUES ET DE PHYSICO-CHIMIE POUR L'ENVIRONNEMENT ET LES MATERIAUX
MIO Institut Méditerranéen d'océanologie
BIC Bordeaux Imaging Center
Help of the ANR 617,705 euros
Beginning and duration of the scientific project: December 2021 - 48 Months